It is well known in the art to use suitably engineered diagnostic, therapeutic, and surgical ophthalmic lenses to provide an indirect image of the retina of a patient while under examination. By properly placing such a lens its designed working distance away from the corneal surface, an indirect image of the retinal surface is formed external to the eye structure. The indirect image of the curved retinal surface is typically formed in a generally flat image plane wherein it is available for convenient observation via one of many types of ophthalmic imaging devices that are known in the art—surgical stereomicroscopes and slit lamp stereomicroscopes being examples of such imaging devices.
U.S. Pat. No. 4,627,694 describes a lens that is designed to be used in conjunction with a slit lamp stereomicroscope to facilitate a diagnostic examination of a patient's retina during a standard office visit. This patent describes the use of a symmetrical double aspheric lens that, when positioned a prescribed distance away from the surface of the cornea, acts to form an indirect or aerial image of the patient's retina. This type of lens is often described as a non-contact ophthalmic lens in that it forms a high-resolution retinal image without requiring the lens to come into direct contact with the patient's eye.
Similarly, U.S. Pat. No. 5,523,810 describes the innovative attributes of one particular implementation of a contact style ophthalmic lens. In this particular implementation, the innovation primarily consists of using a compound contact lens element within the lens assembly. For the specific purpose of illustrating the innovation of the current invention, it is required to highlight that one of the surfaces of the lens assembly described in the U.S. Pat. No. 5,523,810 has been fabricated using a cornea-matching concave radius of curvature. This is done because this type of lens is designed to be placed in direct contact with the patient's eye during use. Another important attribute of the invention described in the U.S. Pat. No. 5,523,810 is the inclusion of a second imaging lens element spaced a distance away from the contact lens element. This second lens element is used in this implementation to collect and focus the light exiting the contact lens element and is primarily responsible for forming the aerial or indirect image of the retinal surface.
In U.S. Pat. No. 5,523,810, a housing is described which is used to securely mount the lens elements in place at a lens spacing that optimizes the image forming capability of the lens assembly. Typically the housing used in an ophthalmic lens assembly such as this takes the form of a contiguous 3-D conical surface manufactured out of an appropriate metal or polymer material. It is typical to affix the contact and imaging lens elements to the housing threaded inserts and epoxy and polymer O-ring sealants. The epoxy and O-ring sealants are used to form a liquid-tight internal spacing cavity between the two lens elements. Constructed in this fashion, the contact style imaging lens assembly of U.S. Pat. No. 5,523,810 is compatible with immersion in water or other appropriate liquid for the purpose of thorough cleaning between uses.
In addition to cleaning, it is essential to sterilize such a contact style ophthalmic lenses between uses to prevent the spread of infectious diseases. For lens assemblies as described in the U.S. Pat. No. 5,523,810 patent, the required sterilization step has historically been achieved using sterilizing gas such as ethylene oxide (ETO). However, it is widely known that there are undesirable attributes associated with ETO sterilization. First off, the per-item costs associated with ETO sterilization are relatively high. In addition, the turnaround time for an item that is sterilized using ETO is relatively long due to a mandatory aeration time that is required to remove the gas residuals that have adhered to the item after it exits the sterilization chamber.
Autoclave sterilization, or high-temperature steam sterilization is becoming the preferred method of sterilizing medical devices because of its inherently low costs, relatively quick turnaround time, and lack of any chemical disposal concerns. Autoclave sterilization is enacted by placing the item that is to be sterilized in a steam environment having a temperature between 120° and 135° and at an over pressure of 200,000 Kpa.
It has been shown that after exposing ophthalmic lenses constructed using epoxy and polymer O-ring sealants (as per U.S. Pat. No. 5,523,810) to a small number of autoclave cycles, water in both liquid and vapor forms begins to encroach into the sealed cavity between the contact and imaging lens elements. While sufficient for sealing out low pressure liquid water, the porosity of epoxies and polymer O-ring seals have been shown to be insufficient to prevent the encroachment of high-temperature/high-pressure steam, as found in an autoclave, into a sealed cavity between adjacent but spaced lens elements. Once water has breached into the internal cavity of a lens so constructed and has condensed onto the internal lens surfaces, those surfaces have to be cleaned and dried of any condensed moisture before the lens can be effectively applied again. Lenses of this type are not well suited for disassembly and cleaning, as they require special tools and disassembly/assembly procedures to facilitate completion of these actions.
U.S. patent application Ser. No. 11/251,112, filed Oct. 14, 2005, describes a multi-element ophthalmic imaging lens that is compatible with a steam autoclave. In this patent application, the concept of opening up the housing body so that there is no longer an internal spacing cavity to collect condensed moisture is introduced and implementation details presented. Constructed in the fashion outlined in the Ser. No. 11/251,112 application, both surfaces of the contact lens element as well as the imaging lens element are exposed to the sterilizing and subsequent drying cycles associated with a complete autoclave cycle. The possibility of moisture permanently encroaching into an internal cavity is therefore eliminated from concern.
While an implementation as described in application Ser. No. 11/251,112 does eliminate the need to effect an autoclave resistant seal on an internal spacing cavity and is therefore suitably autoclavable, an open-cavity design as described in this application does result in the undesirable feature of leaving the opposed contact lens and imaging lens surfaces exposed to the possibility of experiencing fluid splashes or condensation fogging during the course of surgery. The prospect of achieving a hermetically-sealed, autoclave-compatible internal spacing cavity is ideally prescribed for autoclavable ophthalmic imaging lenses.
U.S. Pat. No. 6,695,775 B2 describes a lens assembly for use within autoclavable endoscopes. To address the deficiencies associated with using epoxies or polymer O-rings as sealing agents within autoclavable lens assemblies, U.S. Pat. No. 6,695,775 B2 introduces the innovation of applying, by evaporative coating or by plating, a film of metal to the outside periphery of the physical lens element. Properly prepared in this fashion, metal solder can then be used to hermetically seal the prepared lens element to other properly prepared lens elements or, alternately, directly to a metal mounting structure. By using metal solder, an effective seal can be made that will allow a hermetically sealed internal spacing cavity to be maintained even after multiple exposures to autoclave sterilization.
Though the technology described in U.S. Pat. No. 6,695,775 B2 adequately allows a hermetically-sealed internal spacing cavity to be formed in lens assemblies that are required to be compatible with autoclave sterilization, the evaporative coating/plating processes as well as the laser-based metal soldering process which is required to effect proper sealing are highly specialized. These specialized manufacturing processes require the skilled operation of expensive manufacturing equipment. As a result, a more accessible means of creating an autoclave-compatible hermetic seal for ophthalmic lens assemblies still remains a goal.